The present invention relates to a measuring device, particularly a gas meter, including a measuring mechanism, a counting mechanism, a variable transmission gear assembly provided between the measuring mechanism and the counting mechanism and an adjustment member that engages at the gear assembly for changing the transmission ratio.
The present invention is employed, in particular, for bellows gas meters for measuring the consumption of gas in households. Such bellows gas meters have been used extensively for decades and are manufactured in large numbers for new installations and for the continuous replacement of worn-out devices.
With respect to measuring accuracy, public utilities and its customers place high demands on gas meters. Bellows gas meters which generally are equipped with four alternatingly filling and emptying measuring chambers, measure the volume of gas passing through the meter, while the customer must be charged with the heating value of the gas. However, the density of the gas is a function of temperature; it decreases with increasing temperature. The gas temperature is influenced by the seasonal temperature of the gas supplied to the meter, the plumbing between the main terminal in the house and the meter and the location of the meter within the house.
Measures for compensating the temperature of gas meters have been known for a long time in various embodiments. For example, a measuring device for gas has become known, among others, which is provided with a friction gear assembly between the measuring mechanism and the counting mechanism. This gear assembly includes two mutually offset friction discs and two friction wheels that are coupled together by gears and are displaceable on the friction discs by means of a bimetal controlled rotary slide for the purpose of changing the transmission ratio. Temperature caused changes in the volume of the gas to be measured are compensated by an essentially proportional change in the transmission ratio (European Patent Application 0,197,177.A1). However, this device does not operate without slip nor with little wear and has therefore an adverse influence on the measuring accuracy of the gas meter equipped with it.
A pressurized gas meter is known in which two automatic correction systems are included between a measuring mechanism and a counting mechanism. The mechanical devices for compensating temperature as well as pressure each include continuous blocking mechanisms equipped with latch carriers, latch wheels and cams that are successively included in the transmission path and are controlled through levers and toothed sectors by temperature and pressure boxes. These correction systems are very complicated in design from an engineering point of view and their measuring accuracy is limited (German Patent 841,226).
Also known is a gas meter operating with automatic temperature compensation which includes a continuously variable transmission equipped with two oppositely disposed rotary discs that are in operative connection by way of a roll contact element disposed therebetween. To change the transmission ratio, the one rotary disc is axially displaced relative to the other by a temperature influenced expansion device. This compensation device is also mechanically complicated and, since it does not operate without slip, measuring errors are unavoidable (German Patent 2,813,433).